Diaphragm



Dec. 14, 193 7. A. HAMMER 2,102,150

DIAPHRAGM Filed Dec. 26, 1935 INVENTOR ARTHUR AM MER /fum ATTORN EYPatented Dec. 14, 1937 PATENT OFFICE DIAPHRAGM Arthur Hammer,

Berlin, Germany, assignor to Telefunken Gesellschatt fiir DrahtloseTelegraphic m. tion of Germany b. 1]., Berlin,

Germany, a. corpora- Application December 26, 1935, Serial No. 56,140 InGermany November 6, 1934 4 Claims;

The invention relates to diaphragms of hygroscopic work material such asfibrous material (paper, card board) or similar work material foracoustic apparatus, especially loudspeakers.

The diaphragms produced of hygroscopic work materials such as fibrousmaterials (paper) or similar work materials and composed of individualparts in the ordinary manner, or produced in accordance with the castingor moulding method, have the disadvantage that they are capable ofabsorbing from the air a comparatively large amount of water. At varyinghumidity of the air there also varies the moisture content ofthediaphragm. Under these influences the diaphragm is continuouslysubjected to variations and buckles whereby the initial shape of thediaphragm will no longer be retained. Due to the deformations of thediaphragm the reproduction of loudspeakers in which such diaphragms aremounted, is considerably disturbed since the parts connected with thediaphragm such as mount and drive are moved out of their initialposition. Thus in dynamic loudspeakers for instance, the oscillatory orvoice coil may be 25 placed against the poles of the magnet system andgives cause to microphonic effects. Also considerably non-lineardistortions may occur during the reproduction.

It has been proposed to avoid the deformations of diaphragms due to thevarying amount of humidity, to cover the finished diaphragms withlacquer. Generally, artificial lacquers, or lacquers of natural resinare used, and which after being applied to the diaphragms, areordinarily subjected to a heat treatment. Since these lac quers howeverbegin to crack in time, water enters the very fine cracks and penetratesin considerable amount into the material of the dia- 40 high absorptionof water the diaphragm material performs such'inner action, that aproper operation with diaphragms treated in such manner is not possible.

Due to the treatment of the surface of the diaphragm with the knownlacquers, the acoustic performance of the diaphragms will be verygreatly varied. The lacquers become very hard in the course of time,thus considerably solidifying the surface layers of the diaphragm.Furthermore, also the individual fibers on the surface of the diaphragmwill be highly hardened. As a result thereof the inner damping of theactual diaphragm material will be highly reduced since the individualparts of the fibers can.

phragm due to capillary action. In view of the no longer displacethemselves relative to each other. This condition produces an essentialincrease in the formation of distinct partial oscillations of thediaphragm whereby the reproduction is detrimentally affected.

In accordance with the invention the absorption of humidity by thediaphragms will be avoided by treating the diaphragms wholly orpartially by means opposing water or insoluble in water. Among thesemeans may be mentioned for instance water soluble vinaigrous pottersclay, furthermore, albuminous solutions which are subsequently hardenedby means of chromates or bi-chromates or the like. The treatment can becarried out in such manner that the mentioned means are applied orsprayed on the finished diaphragm in a liquid state or the diaphragmsare totally or partially impregnated therewith. It is also possible toadd the solutions simultaneously to the diaphragm material to be workedwhen producing the diaphragm.

As already stated above it will thereby be accomplished that absorptionof moisture fromthe air by the diaphragm is practically completelyavoided. It is thus no longer possible that the diaphragms continue toact under the influence of the varying moisture content of the air, inother words, they will no longer buckle, but retain the shapes in whichthey were originally formed.

In treating the diaphragm with the mentioned means the desired increasein the mechanical strength of the diaphragm is obtained, yet thecharacteristic properties of the work material or of the individualfibers are retained, i. e. the inner damping of the diaphragm ispractically not at all decreased or only to an unessential degreerelative the inner damping of a non-treated diaphragm so that partialoscillations at repro duction will no longer be noticed in a disturbingmanner. These means have the advantage over the usually employedlacquers that they enter into the structure of the diaphragm and intotheir fibers without changing the structure of the diaphragm so that themovability'of the individual fibers of the work material of thediaphragm will be changed only to an unessential degree relative to thecondition of the nontreated diaphragms.

Figures 1, 2, and 3 of the drawing show various examples of embodimentsof diaphragms for electro-dynamic systems preferably produced accordingto the casting or moulding method. The diaphragms may, however, also becomposed of. individual parts connected with each other.

inplacelof the electro-rlynamic drive system,

obviously, also an electro-magnetic system, that is, one provided with a'moving armature, or

any other drive system may be employed. Corinto corrugations 2terminating into an upper rim 3., Thereis fastened to the diaphragm ifthe coil body i which carries thvoice coil windins The surface of thediaphragm i and the mount'consisting of the corrugations 2; as well-- asthe diaphragm rim 3 are totally or partially treated with the meansopposing moisture above described.

Figure 2 shows an example of an embodiment) of freely radiating conediaphragm for dynamic loudspeakers. In this example a special alignmentspiral 6 forms an exterior centralizing means.

aioaioo I J I Figure 3 is a iurther example'for an"embodimerit oi adiaphragm having a complex shape and in which in place of an exteriorcentrali'zing means for the oscillatory coil anlnner centraiiz'mg meansi is chosen.

at I claim is: p

1. A frliaphragrn for acoustic devices made from moulriabie fibrousmaterial-which has been treated with an albuminous solution.

2. A diaphragm for acoustic devices made. from mouldaiole fibrousmaterial which has been treated with an alhuminous solution containingchromates.

11A diaphragm for acoustic devices made from' niouidable fibrousmaterial which is impregnatetl with an aibumirious solution contain-.

ing chromates.

an diaphragm for acoustic devices made from mouldabie fibrous materialand coated with an albuminous solution containing chromates. 20

